The present invention relates to a laser drilling method and a laser drilling apparatus for carrying out drilling by irradiating works such as printed circuit boards and ceramic substrates with a laser beam from a laser oscillator.
With trends toward miniaturization and high-density mounting of electronic components, high density is required for printed circuit boards. For example, an interposer is known as a printed circuit board for mounting and packaging LSI chips. Although connection between such LSI chips and the interposer has been primarily performed by wire bonding processes, flip-chip mounting is increasing and furthermore, the number of pins in packages is increasing. With such trends, holes which are called via holes must be provided in small diameters and in fine pitches in the interposer.
Although such drilling has been performed by a mechanical machining process using a fine mechanical drill or by an exposure (photo-via) process, laser beams start to be used nowadays. Drilling apparatuses using laser beams are superior to mechanical machining using fine drills in view of processing rate and ready formation of finer holes. As laser beam sources, CO2 lasers and harmonic solid-state lasers are generally used because of the inexpensiveness of the laser oscillator and reduced running costs.
Problems to be Solved by the Invention
In the conventional laser drilling apparatus, the laser beam from the laser oscillator is introduced to an optical scanning system having biaxial galvano-mirrors called an X-Y scanner or galvano-scanner via an optical path including a reflecting mirror and the like. The drilling is carried out by scanning the laser beam by the optical scanning system and by irradiating a printed circuit board with the laser beam through a processing lens (for example, Japanese Unexamined Patent Publication No. Tokkai-Hei 10-58178). Since the positions of holes to be formed in the printed circuit board are determined preliminarily, the drilling is carried out one by one by controlling the optical scanning system in accordance with the information of the positions of these holes.
However, in the one-by-one drilling using the optical scanning system having the X-Y scanner or galvano-scanner, the processing time increases in proportion to the increment of the number of the holes in the printed circuit board. By the way, since the response of the galvano-scanner is about 500 pps, it is difficult to form 500 or more holes per second. Supposing that holes with a diameter of 50 xcexcm are arranged at a pitch of 0.2 mm in a square package board with a side length of 10 mm, the number of the holes is 2,500. In this case, the processing time is required by 2,500/500=5 sec, even if the drilling with a drilling rate of 500 holes/sec is carried out.
Accordingly, an object of the present invention is to provide a laser drilling method that can form many holes within a shorter time compared with known laser drilling methods.
Another object of the present invention is to provide a laser drilling apparatus suitable for the above method.
The present invention is a laser drilling method for carrying out drilling by irradiating a workpiece with a laser beam from a laser oscillator. According to an aspect of the present invention, in the drilling method, the laser beam is projected traveling through a polygon mirror, a mask having a mask pattern including a plurality of holes for defining a processing pattern, at least one galvano-mirror, and a processing lens. The polygon mirror sweeps the laser beam so that the laser beam scans across the plurality of holes in the mask to thereby forming a plurality of holes into the workpiece. An irradiation region of the laser beam onto the workpiece is shifted in one axis direction by the at least one galvano-mirror.
In a laser drilling method according to another aspect of the present invention, the laser beam is projected traveling through a shaping optical system for shaping the laser beam into a line or rectangle, a polygon mirror, a mask having a mask pattern including a plurality of holes for defining a processing pattern, at least one galvano-mirror, and a processing lens. The polygon mirror sweeps the laser beam so that the laser beam scans across the plurality of holes in the mask to thereby collectively forming a plurality of holes into the workpiece. An irradiation region of the laser beam is shifted in one axis direction by the at least one galvano-mirror.
According to the present invention, a laser drilling apparatus for carrying out drilling by irradiating a workplace with a laser beam from a laser oscillator is provided. In the drilling apparatus, a polygon mirror, a mask having a mask pattern including a plurality of holes for defining a processing pattern, at least one galvano-mirror, and a processing lens are arranged between the laser oscillator and the workpiece. The laser beam from the laser oscillator is projected onto the workpiece traveling through these components. The polygon mirror sweeps the laser beam so that the laser beam scans across the plurality of holes in the mask to thereby forming a plurality of holes into the workpiece. An irradiation region of the laser beam is shifted in one axis direction by the at least one galvano-mirror.
In a laser drilling apparatus according to another aspect of the present invention, a shaping optical system for shaping the laser beam into a line or rectangle, a polygon mirror, a mask having a mask pattern including a plurality of holes for defining a processing pattern, at least one galvano-mirror, and a processing lens are arranged between the laser oscillator and the workpiece.
In any above-mentioned laser drilling apparatus, in case of providing two galvano-mirrors, the irradiation region of the laser beam onto the workpiece is shifted by one of the galvano-mirrors in one axis direction while the irradiation region of the laser beam onto the workpiece is shifted by other one of the galvano-mirrors in the direction which is orthogonal to the one axis direction.
In the laser drilling apparatus according to the above-mentioned other aspect, a masking mechanism is preferably arranged in an optical path between the laser oscillator and the mask to avoid the irradiation of the laser beam during shifting the irradiation region of the laser beam.